If you are using firmware versions 4.11.011 or earlier, it is recommended that when changing to IP address to do it separately from other configurations changes. In other words, change the IP address only and do not make other configuration changes until after the reboot.
Also use the “OK to power down” button on the router setup page to see if the flash as been updated before rebooting. Do not change configuration information on other pages on the same flash write reboot cycle. There is a problem with firmware versions 4.11.011 and earlier where flash might be corrupted if the specifications are not followed. This has been fixed in version 4.12.050 and later.